Shaped and tempered glass sheets are widely used as side windows or rear windows in vehicles such as automobiles or the like, and, to be suitable for such application, flat glass sheets must be shaped to precisely defined curvatures dictated by the shape and outline of the frames defining the window openings into which the glass side or rear windows are installed. It is also important that the rear or side windows meet stringent optical requirements and that the windows be free of optical defects that would tend to interfere with the clear viewing therethrough in the viewing area. Any distortion in shaping members that engages a heat softened sheet to help shape the latter is replicated in the major surface of the sheet and may result in an optically deficient surface of the shaped sheet.
One type of commercial production of shaped glass sheets for such purposes commonly includes heating flat glass sheets to their softening point, shaping the heated sheets to a desired curvature and then cooling the bent glass sheets in a controlled manner to a temperature below the annealing range of the glass. During such treatment, a glass sheet is conveyed along a substantially horizontal path that extends through a tunnel-type furnace where the glass sheet is one of a series of sheets that are heated to a deformation temperature of glass and along an extension of the path into a shaping station where each glass sheet, in turn, is engaged by a vacuum mold. The vacuum mold lifts and holds the heat softened glass sheet by suction. At about the same time, a transfer and tempering ring having an outline shape conforming to that desired for the glass sheet, slightly inboard of its perimeter moves upstream into a position below the vacuum mold. The vacuum releases and deposits the glass sheet onto the tempering ring. The tempering ring supports the peripheral edge of the glass sheet while it conveys the glass sheet into a cooling station for rapid cooling.
The vacuum mold is provided with a curved shaping surface that shapes the heat softened glass sheet by suction thereagainst. The molds are generally constructed of a ceramic block or a metal vacuum box. Apertures in the block or the metal shaping plate of the vacuum box connect to a hollow vacuum chamber which communicates with a vacuum source. The mold is covered with a refractory material such as a fiber glass cloth that will not mar or harm the glass at elevated temperatures.
It would be advantageous to construct a vacuum mold with an adjustable shaping surface that can easily change the shaping curvature of the mold without having to replace or disassemble the vacuum mold.